Here we dive into some proposals for what comes later, when the basics of the GpsQuests are in place.
People need to be motivated to complete more quests, and to interact with the community. The easiest way to do that is to track the completion of quests, show statistics of how many quests have been done and when - this can be taken directly from the stats options provided by regular geocaches.
In a similar way, the authors need to be rewarded for creating great quests, and the easiest way to do this is to show how popular they are, and how many "likes" or favourite points they get awarded. But of course questers can't award favourite points to every quest they complete, otherwise they become meaningless, so there needs to be a certain number of quests completed before one of them can be awarded a favourite point (or star or whatever).
It has been suggested that each quester could be made automatically part of a team, or a tribe. Probably this is assigned at random? Possibly it's just a meaningless tribe designation like a colour, or maybe it's like a Hogwarts House with a certain symbol or flag or logo, maybe it's something like an elemental symbol (fire, earth, air, water). This could make it more of a collective experience rather than a series of solo experiences.
In this way, when a quester completes a quest, they do it for themselves and their own statistics, obviously, but they also do it for their team. For each quest on the map, it can be shown with the logo of the most recent team to complete it. If another team completes it, the quest gets their logo instead, possibly encouraging someone from the first team to "win it back" by completing it on behalf of their team.
In order to decide whether to attempt a quest or not, it might be useful for each to have certain properties, like a difficulty level, an estimated completion time, an estimated travel distance (maybe I'm not in the mood for a 10 km quest right now!), and maybe other attributes. In conjunction with the popularity of course.
There may even be different quest types, for example a simple orienteering race, a magical puzzle, an informative tour, a silly game or perhaps other categories. Perhaps the race-type quests have time limits or a best time record.
People need to be encouraged and rewarded for creating quests. One way to do this could be to award badges, a bit like those on StackOverflow or other such community efforts which rely on volunteer contributions. Badges cost nothing to award, but they give bragging rights for various aspects of contributing to the quests, whether it's completing a certain number, or authoring the first one, or resurrecting a quest which hasn't been completed for some time, or writing a quest review or whatever.